The present invention relates to a digital-data recording and reproducing apparatus, and more particularly to a spindle-motor control circuit for rotating an optical disk or the like.
When tracking of a disk having digital signals recorded by a constant linear velocity (CLV) method is performed by using an optical pickup, the disk is rotated in such a manner that the rotational speed is lowered as the optical pickup is moved from the inner portion of the disk to the outer portion of the disk. The control of the rotational speed is performed by controlling the rotational speed of the spindle motor in such a manner that the frequency of synchronizing clocks (clocks generated by a phase locked loop circuit in accordance with the reproduced signal) synchronized with signals reproduced from the disk is made to be a predetermined frequency.
When any synchronizing signal cannot be obtained in the above-mentioned case, for example, when rotations of the motor have been started or when the optical pickup is moved at high speed, a maximum value (the longest inversion interval) in the interval from a rising edge of the reproduced signal from the disk to the falling edge of the same or the interval from the falling edge to the rising edge is detected. Then, the rotational speed of the spindle motor is controlled in such a manner that the longest inversion interval is made to be a predetermined value. The foregoing is disclosed in Postexamined Japanese Patent Publication No. 4-71269.
The magneto-optical disk or the like has wobbling (a zigzag guide groove or land) for use in tracking which is required when data is recorded or in detecting the recording position. Moreover, the minidisk (MD) includes address information in the wobbling portion. When the wobbling is used, also control of the rotations of the spindle motor can be performed. Such control will now be described in an example case of a DVD-RAM disk.
FIG. 15 is a block diagram showing a circuit for controlling a spindle motor adapted to a DVD-RAM disk. Reference numeral 1 represents a disk, 2 represents an optical pickup, 3 represents a spindle motor, 4 represents an operation amplifier for rotating the spindle motor, 5 represents an analog signal processing circuit for equalizing a reproduced signal and extracting a wobble signal, 6 represents a digital signal processing circuit for digital-processing the reproduced signal, 7 represents a channel-clock generating circuit for generating a channel clock for performing recording by multiplying the wobble signal, 8 represents a frequency comparator, 9 represents a phase comparator, 10 represents a calculator and 11 represents a PWM-signal generating circuit.
Operation of the circuit shown in FIG. 15 will now be described. When the disk 1 has been rotated by the operation amplifier 4 and thus a reproduced signal has been read by the optical pickup 2, a wobble signal is extracted by the analog signal processing circuit 5. Moreover, data in the reproduced signal is processed by the digital signal processing circuit 6 so as to be transmitted. Moreover, the extracted wobble signal is supplied to the channel-clock generating circuit 7; The channel-clock generating circuit 7 is, as shown in FIG. 16, in the form of a phase locked loop (PLL) circuit composed of a voltage control oscillator (VCO) 12, a frequency divider 13 for dividing the output signal from the VCO 12, a phase comparator 14 for subjecting the phases of the output of the frequency divider 13 and the supplied wobble signal to a comparison, a frequency comparator 15 and a low pass filter 16. The structure is shown in FIG. 16.
The operation of the channel-clock generating circuit 7 will now be described. Since the DVD-RAM disk is structured in such a manner that the channel clock (the clock for reading/writing data) is an integral multiple of the wobble signal, the clock transmitted from the VCO 12 is divided at a division ratio which corresponds to two times the division ratio of the frequency divider 13. Then, the output of the frequency divider 13 and the supplied wobble signal are supplied to the phase comparator 14 and the frequency comparator 15, respectively.
Since the frequency of the supplied wobble signal varies depending on the number of revolutions of the disk 1 and the reading position set to the optical pickup 2, the amount of the change is communicated from the phase comparator 14 as an error signal. Similarly, a phase difference component is communicated from the frequency comparator 15 as an error signal. The two error signals are added to each other, and then converted into an error voltage signal by charging/discharging a capacitor or the like by the low pass filter 16, the error voltage signal being supplied to the VCO 12. The oscillated frequency of the VCO 12 is changed to cancel the supplied error voltage. As described above, a closed loop is formed in which the clock transmitted from the VCO 12 is synchronized with the supplied wobble signal.
The clock synchronized with the supplied wobble signal and transmitted from the VCO 12 is divided to 1/2 by the frequency divider 13 so as to be fetched as a channel clock. The channel clock is supplied to the next frequency comparator 8. The channel clock is also employed as a clock for transmitting data to be recorded when a recording operation is performed.
On the other hand, the DVD-RAM disk is structured in such a manner that the frequency of the channel clock is 29.18MHz in a case where the disk 1 is rotated at constant linear velocity. Therefore, a clock having the above-mentioned frequency is, as a reference clock, supplied from a crystal oscillator or the like to the frequency comparator 8. The frequency comparator 8 subjects the channel clock fetched from the channel-clock generating circuit 7 and the frequency of the reference clock to a comparison so that a signal indicating the error in the frequency is transmitted.
The phase comparator 9 is, similarly to the frequency comparator 8, supplied with the reference clock having the frequency of 29.18 MHz from the crystal oscillator or the like. The reference clock is divided with the division ratio corresponding to 1/2 of the division ratio of the channel clock and the wobble signal in the frequency divider 13. The divided frequency of the clock is made to be the same as the frequency of the wobble signal when the disk 1 is rotated at constant linear velocity. The division signal and the wobble signal transmitted from the analog signal processing circuit 5 are subjected to a comparison by the phase comparator 9 so that a signal indicating the error in the phase is transmitted.
Both of the frequency error signal and the phase error signal are supplied to the calculator 10 so as to be multiplied with a real number so that the gain is adjusted. Then, the signals are added to each other, and then transmitted. The output of the error signal from the calculator 10 is supplied to the PWM-signal generating circuit 11 so as to be subjected to PWM (Pulse Width Modulation), and then supplied to the operation amplifier 4. Since the number of revolutions of the spindle motor 3 is controlled in such a manner that the error signal subjected to the PWM and transmitted from the operation amplifier 4 is canceled, the disk 1 is rotated at the constant linear velocity.
As described above, the rotations of the spindle motor 3 adapted to the DVD-RAM disk can be controlled by using the wobble signal. Therefore, an effective result can be obtained when data is recorded on the disk 1.
However, the clock synchronized with data can be obtained from the reproduced signal by a conventional PLL circuit adapted to data during the reproducing operation, furthermore accurate control can be performed. In this case, the frequencies or the phases of the synchronized clock and the reference clock (29.18 MHz) generated by the crystal oscillator or the like are subjected to a comparison to obtain an error signal so as to control the rotations of the spindle motor. Moreover, a countermeasure must be taken against a case in which the wobble signal is not supplied because of, for example, deviation of the optical pickup 2 from the track. Thus, the foregoing problems arise.